The DNA sequence of a wood-munching marauder - Sanger Institute

A call to arms

The tapping sound of the adult Deathwatch Beetle, Xestobium rufovillosum, a wood-boring insect, was traditionally meant to be bad luck, heralding tragedy in a household. Often heard in the quiet of the night, it was thought to be a countdown to death1. Ironically, the ominous sound of the tapping adult beetle is actually a beetle duet between male and female adult beetles who tap to find mates in order to carry on the Deathwatch Beetle line2.

Out of the wood and into the lab, researchers from the Wellcome Sanger Institute have sequenced the genome of the Deathwatch Beetle for the first time. Armed with the genome sequence of the Deathwatch Beetle, researchers at the University of Oxford, Cranfield University, and the National Museum of the Royal Navy have joined forces to further the study of the Deathwatch Beetle. Their aim is to assist with ongoing conservation efforts, better understand the beetle’s behaviour, biology and preserve the historic British warship HMS Victory.

From ancient woodland to invading prized historical monuments

In nature, Deathwatch Beetles are attracted to damp wood. Researchers are unsure what it is that attracts the beetles, whether it is something the wood gives off, or something the fungi decaying the wood gives off, or a combination of the two. The female beetle lays 40-80 eggs and the larvae develop within rotting timber. The larval stage of the beetle is poorly understood but can last up to 13 years, and results in extensive tunnels throughout the decaying wood. This tunnelling behaviour creates a network of corridors so extensive it can be structurally destructive. This is helpful in an oak woodland where decomposing trees are essential for a healthy ecosystem. This is not helpful in a historic wooden monument.

It is not just HMS Victory that is at risk; any wooden (typically oak) structure can be affected. In addition to HMS Victory, Westminster Hall fell victim3, with tunnelled out cavities discovered to be large enough to fit an adult human. It’s clear that the beetle is a true destroyer if given the right conditions, and preservation efforts have had limited success. Cathryn Harvey, a Deathwatch Beetle expert and Ph.D. student at the University of Cranfield, is studying a 70-year-old replacement plank from the deck of HMS Victory. She has estimated that nearly 40 per cent of the plank has been eaten away. This would indicate that unless eradication of the Deathwatch Beetle is successful, there will come a time when no original wood is left on the ship.

Diana Davis, Head of Conservation at the National Museum of the Royal Navy, says: “Although the amount of historic timber that one beetle eats is small, over a period of a hundred years that damage begins to look more significant.” 

Managing the risk of the beetles’ presence and a desire to know more about what they are up against has led to a collaboration between the National Museum of the Royal Navy and Cathryn’s Ph.D. project at the Cranfield University.

From uninvited interlopers to research VIPs

To aid ongoing conservation efforts Cathryn, a conservator by training, is studying the Deathwatch Beetle tunnelling behaviour as part of her doctoral research. Cathryn’s studies are funded jointly by Cranfield University and the National Museum of the Royal Navy. She is closely examining infected wood from HMS Victory using the latest technology; she’s been able to get glimpses into the larva trajectory to learn more about its behaviour. Cathryn uses a 3D imaging technique called Micro-CT also known as micro computed tomography. Micro-CT utilizes X-rays to see inside an object. Micro-CT is much like a hospital CT scan but on a much smaller scale with results appearing in greater resolution. Using this technology gives Cathryn and collaborators a glimpse into the larvae’s development and behaviour.

Cathryn’s aim is to build the foundation of knowledge and expertise needed to understand the Deathwatch Beetles’ hidden life under the surface of infested wood. She can then apply her expertise to better predict the larvae’s path through the wood it is eating. Additional research is also being carried out at the Zoological Society of London (ZSL). They are rearing beetles on a section of HMS Victory timber, which they hope to open to the public in the future for education purposes.

Cathryn and colleagues have been testing non-invasive techniques for detecting the larvae in the timbers with the ZSL colony and on HMS Victory. The use of acoustic equipment could assist researchers in discovering the location of the beetles to target conservation work. Her research encompasses both listening to the wood for the movement of the larvae as they munch through wood, and listening for the distinctive tap, tap, tap of the romance-seeking adult beetles. As Cathryn discovered, the Deathwatch Beetle isn’t fussy when finding a mate. “When we tap on the laboratory table, the beetles tap back,” she says. Acoustics along with the genome may be one more piece of the puzzle to better understand the Deathwatch Beetle.

To bring the battle against the beetle into the genomic era, adult beetles were collected by the National Museum of the Royal Navy’s Conservation team before being transferred to University of Oxford researchers for the first stage of sample preparation.

Peak adult beetle emergence occurs on HMS Victory around April-June when temperatures rise above 10 ̊C. Diana explains: “We keep a record of locations and numbers of beetles to help us track the activity on the ship.” Next, the adult beetle samples were prepared for whole genome sequencing at the Sanger Institute. Following DNA extraction, sequencing, assembly and annotation, the result is the first genome sequence of the Deathwatch Beetle openly accessible to the public and researchers. The genome could open new areas of research and accelerate ongoing research into the beetle’s behaviour.

Genomic weapon in battling the beetle

HMS Victory is currently in the midst of a huge conservation effort to save it for future generations. The National Museum of the Royal Navy have been studying the Deathwatch Beetle for years  to learn about the risks they pose to the ship and to de-code the damage caused by this historic infestation, which goes back at least 100 years.

Diana says, “We initially approached the Tree of Life programme because we need to understand whether the beetles on the ship come from a single infestation or several separate attacks.” 

 

A complete genome sequence of the Deathwatch Beetle will allow researchers to pinpoint the infestation timeline and the physiology and population dynamics of this important species5.

The genome sequence itself should also tell scientists and conservators much about the physiology and biochemistry of the species. As Peter Holland, Department of Biology, University of Oxford, explained, “We don’t really know how the Deathwatch Beetle hones in on fungal-infected wood, we don’t know how the larva digests wood or whether this requires interactions with bacteria. The genome sequence will show us all the genes encoding olfactory receptors, digestive enzymes and much more. We get a direct route to the physiology of the species.” And this is where having genomes for 150 other beetle species, or 3000 other insects, also becomes critical. 

Peter Holland added, “The Darwin Tree of Life project enables comparative genomic biology. We would never be able to spot the specific adaptations of one species unless we compare it to its relatives – we can now peer into the evolutionary history of every Deathwatch Beetle gene.”

With the first Deathwatch Beetle reference genome sequence as a guide, scientists now have another tool in their belt while battling to protect historic buildings and ships – but there is still much work to do. Next time the Deathwatch Beetle comes knocking, we’ll be better prepared to answer with its DNA sequence to hand.